The present invention relates to transfer of data used in a system for transferring data among a plurality of information processing devices, and in particular to a data processor and a data transfer method, responsive to need of some conversion or data processing between recorded data and data needed at transfer destination, for conducting a series of processing from data readout to processing and transfer most efficiently.
In case data are transmitted from a certain terminal to another terminal, it is necessary to make the transmission management scheme of the transmission data description scheme (such as the head structure, coding scheme, and coding default condition) and the transmission data transmission scheme (such as protocol) coincide between the transmitting side and the receiving side.
Especially if transmitted data are images which are not coded such as text data, then the number of pixels of an image which can be displayed at the transmission destination and the number of colors which can be used are limited by display specifications of an apparatus of transmission destination. In case a plurality of apparatuses are connected via a network and stored image data are transferred to a different apparatus and displayed, therefore, specifications of the stored image data are different from specifications of the displaying apparatus. In order to absorb difference in specifications in some place in the system, it is necessary in this case to effect conversion on the image data itself. Such a problem exists for not only images (such as still pictures and moving pictures) but also data which are difficult to code such as speech.
In case image data or the like other than coded data were transmitted between different terminal apparatuses, therefore, conventionally a converter for matching the transmission management scheme was individually built in each terminal apparatus of the transmitting side and transmission data matched to the transmission management scheme of the terminal apparatus of the receiving side were generated by the terminal apparatus of the transmitting side and transmitted to the terminal apparatus of the receiving side. On the other hand, conversion relating to contents of image data depended upon specifications and purpose of use of the transmission destination and hence successive conversion was conducted at the transmission destination.
Herein, an apparatus storing and transmitting data is referred to as server, and an apparatus of the receiving side issuing a transmission request and receiving data is referred to as client. It is now assumed that not only such a system configuration that a plurality of servers and a plurality of clients are connected to a network but also such a system configuration that a server is associated with a client in a one-to-one correspondence is included.
Herein, conversion of transmission management scheme and data conversion are collectively referred to as conversion unless especially specified.
Recently, the environment of the client-server system (CSS), in which a plurality of clients and a plurality of servers are connected to a communication network and image data are transferred via the communication network, is now being arranged. In case a system is constructed by using a plurality of apparatuses having different performance and specifications and image data are transmitted, however, the above described conventional technique causes the following problems.
(1) In case the processing speed of a client is significantly lower than the processing speed of a server, processing time is sometimes wasted if complicated data processing is conducted on the client side; PA1 (2) In case a server is accessed from a large number of clients simultaneously, response performance to all clients is degraded if conversion is carried out on the server side one by one; PA1 (3) In case an image having a large number of pixels is transferred and displayed in an apparatus having a low resolution, the coefficient of utilization of the network is lowered if data conversion is carried out on the client side, because a large amount of data must be transferred via the network although they are not displayed; PA1 (4) In case a part of processing is executed by hardware for achieving a higher speed, hardware is mounted on every client and expensive facility cost is needed if processing is conducted on the client side; PA1 (5) In case clients individually cope with data conversion, an operator must grasp parameters concerning the conversion in effecting conversion processing; and PA1 (6) In case, for example, data are stored by using a scheme the client side cannot cope with, operators must individually cope with processing for which various schemes such as a coding scheme exist.